In connection with the fractionated distillation of petroleum crude, there is a residue after the heating oil fractions have been distilled off, which essentially consists of asphalt, bitumen and wax, as well as of so-called heavy oil having a boiling temperature above 350.degree. C. This heavy oil can be further processed into different products, such as spindle and lubricating oils, solvates, softeners, components of solvents with high boiling points, and so forth.
For decades, certain fractions of these heavy oils have been used in the printing industry as components of printing inks. In addition, these fractions are also used in rubber and caoutchouc processing as softeners.
These so-called extracts or fractions, used by the industry in large amounts, are still extraordinarily inexpensive, so up to now there has been little discussion regarding their replacement by other substances. Also, up to a relatively short time ago there has been no detailed research regarding the composition of these distillation products or solvent extracts; such research has only been conducted very recently and has had the result, surprising even to experts, that some of the extracts contain up to 40% or 50% of PCAs (in accordance with IP 346).
Polycyclic aromatic compounds ("PCAs") are understood by the art to be aromatic compounds with condensed closed chain systems, many or almost all of which have proven to be carcinogens or at least co-carcinogens. Examples of these are benzo[a]pyrene and methylcholanthrene. The carcinogenic properties of individual compounds appear to be linked to the presence of so-called bay regions; extensive research by Lowe et al. is available in Accounts Chem. Res., 17, (1984), 332 et seq. Furthermore, it is also known that many PCAs also trigger mutagenic effects and may furthermore be phototoxic. Thus, it is highly desirable to minimize contact with such compounds.
For example, five PCAs have been included in Section III A2 of Germany's the "Draft of the Second Change of the Gefahrstoffverordnung," i.e. "Dangerous Materials Law" because of these properties. Accordingly, it is highly desirable to minimize the release of these potential carcinogens into the environment.
Therefore attempts have been made by the prior art to replace the customarily used extracts by other hydrocarbons, but all these attempts have to a great extend failed because the replacement oils have shown technical disadvantages in the printing ink industry as well as in the rubber industry, which technical deficiencies have reduced their usefulness completely or to a very large degree. For example, it is known that alternative oils of essentially paraffin-naphthene structure are less satisfactory as softeners for most synthetic rubbers because they have only a small compatibility with rubber, so that there is danger of bleeding of the softener from the compound in the course of the vulcanization process. Therefore such mineral oils are less compatible in IR, SBR, BR, NBR, CR and NR rubbers. Similar deficiencies have been found in the replacement oils used in the printing ink industry. For example, it is known that a large portion of paraffins is incompatible with the resins/carbon blacks, etc. used in printing inks.
Therefore there still is a need for a hydrocarbon composition as an alternative or replacement for the sump distillates or extracts used up to now, for example, in the rubber industry or in the production of printing inks. The present invention seeks to overcome these problems of prior art replacement oils through the formulation of compositions, predominantly made up of naphthenic-aromatic hydrocarbon compounds.